flags = isstrdigit( str, M, N )
Function that determines for a given string 'str' if some of its characters represent digits from 0 to 9.
If 'M' and 'N' are not specified, all positions are tested by default.
The output 'flags' will be the size of input 'str', with each position set as 0 where no digit was found or 1 otherwise.
If 'M' is specified and 'N' is not, the only position tested in the string is given by the position in 'M'.
The output 'flags' will be returned as '0' if no digit is found, or '1' otherwise.
If both 'M' and 'N' are specified, positions from 'M' to 'N' are tested.
The output 'flags' will be the size of input 'str', with each position set as '0' where no digit was found or '1' otherwise.
Any untested position will be set as 'NaN'.
If 'str' is a multidimensional array, for each row all columns are counted until 'M' and 'N' are found.
The Matlab built-in function 'isstrprop' can be used to do this, but works a different way.